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Little AC (RV roof unit) help

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dcg9381

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I'm getting roped into to working on an RV. Rear AC isn't working. Compressor is running. Took the cover off, the fan will spin if you get it started, so I assume it's the capacitor.

Diagram. It looks like the small capacitor is for the fan (from the diagram), but the B8865 Capacitor indicates connections for a fan:

1777302048646.png
There are two capacitors here.
1777302082726.png



1777301840033.png
 

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Ohmthis

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The small capacitor is a start capacitor for the compressor. It should drop out after the starting amps drop. The dual cap capacitor is a run capacitor and is in the circuit all of the time. Test the capacitor, that will be the best advice.
 
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dcg9381

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Ok, so I got up there today and replaced the large cap. First think I see is that "CB8865" apparently comes in a variety and I did it wrong..

Old cap: 55uF/15uf@380V
New cap: 45uF+5uF@450V

I only zapped myself once...

So I'll order the 55uF/15

1777556035666.png


Did the same thing, fan on (no compressor), motor would hum, I just give it a spin and it's good to go. Fan spins freely when off...

I took a look at the "little capacitor" under there, it's a "motor start capacitor" - I assume this is compressor?

1777556013490.png



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Dometic says:
1777556753394.png
 
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mm08822

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Putting the same uF value caps back in is better for motor winding life. A higher voltage rating is ok, however, just dont go lower.

Two single value caps can be used if there is room to accommodate instead of a dual cap. Either as permanent fix or temp.

Buy a spare and leave it inside the unit or some place you can find it 10 years from now.
 
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dcg9381

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mm08822 said:
Putting the same uF value caps back in is better for motor winding life. A higher voltage rating is ok, however, just dont go lower.
Click to expand...
Yep, I'm replacing both. My bad for assuming the same part number would be same capacity.
mm08822 said:
Buy a spare and leave it inside the unit or some place you can find it 10 years from now.
Click to expand...
Just trying to get thing working so I can get rid of it.. :)
 
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Al G

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I just replaced the capacitor in one of my units. The original was 1499-576. I ordered one with that model number and the exact electrical specs. Went to put it in and it was 3/4" longer and wouldn't fit. Did some more searching on line and found one the same size as the original. Same number but different physical size. I didn't expect that.
 
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Countyroadtrailers

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dcg9381 said:
On RV AC units, there is only one fan motor. It does both.
I think the smaller cap may be a "soft start" for the AC compressor.

1777305082116.png
Click to expand...
Not the case anymore about one fan for all RVs but for many older units like his 2nd gen penguin there that’s true.
 
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Countyroadtrailers

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dcg9381 said:
I'm getting roped into to working on an RV. Rear AC isn't working. Compressor is running. Took the cover off, the fan will spin if you get it started, so I assume it's the capacitor.

Diagram. It looks like the small capacitor is for the fan (from the diagram), but the B8865 Capacitor indicates connections for a fan:

1777302048646.png
There are two capacitors here.
1777302082726.png



1777301840033.png
Click to expand...
The big capacitor is a two in one combo unit, it handles your compressor run and your combo interior and exterior fan. Specifically the only part of your capacitor that has failed is the 15 uf and in a pinch you could add just a 15 and run a jumper back to the common if you don’t have the right one.

The black unit is your compressor start cap and the other smaller black item is a remote mount ptcr.

Make sure the fan motor spins freely, I would run a capacitance test on the cap but replacement is a good idea if you don’t have a meter that does it. If the motor doesn’t free turn it may not start and in some limited circumstances it may be the motor.

That penguin 2 uses the standard Dometic reversed phone line for communication. Not a bad idea to clean the ends and add some dielectric grease to the ends and the couplers under the unit as they fail a bunch from corrosion.
 
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